A radiation imaging apparatus system includes a radiation generation apparatus and a radiation imaging apparatus including a radiation detection unit, which are oppositely arranged to sandwich an object, and irradiates the object with radiation to acquire image information based on a signal output from the radiation detection unit. Mainly, the radiation imaging apparatus system is widely used in the fields of medical diagnosis and industrial nondestructive inspection.
As a radiation imaging apparatus recently becoming widespread, there is a radiation flat-panel detector. The radiation flat-panel detector includes a combination of a photoelectric conversion panel arraying photoelectric conversion elements for converting visible light into electric charge and switching elements (TFT) in a matrix and a phosphor for converting radiation into visible light. Radiation incident on the radiation flat-panel detector is converted into visible light by the phosphor, and the visible light is converted into electric charge by the photoelectric conversion elements. A built-in electronic circuit performs various processes based on the acquired electric charge to acquire digital image information.
The recent widespread use of the radiation flat-panel detector has been accompanied by more stringent requirements for image quality improvement in the radiation imaging apparatus, miniaturization of the apparatus, stability of a captured image, and durability of the apparatus.
To meet such requirements, a heat generation problem concerning malfunctions or lifetimes of electronic components cannot be avoided, necessitating an efficient heat radiation unit. Efficiently radiating heat enables normal operations of electronic components, guaranteeing of durability, and prevention of characteristic deterioration of a radiation detection unit caused by a temperature increase.
As a conventional technique for heat radiation, Japanese Patent Application Laid-Open No. 10-177224 discusses a method for opening and closing a vent shutter for a heat radiation fan according to a driving condition of a radiation imaging apparatus.
Japanese Patent Application Laid-Open No. 2005-181922 discusses a method for detachably mounting a cooling unit, including a heat radiation fan, on a casing exterior of a radiation imaging apparatus.
The radiation imaging apparatus generally includes electronic components, such as a signal processing unit and a power source, which have heat higher than other electronic components during capturing of a radiation moving image. In the radiation imaging apparatus, a difference in amount of generated heat between various electronic components causes a temperature difference. In many cases, the temperature difference in the radiation imaging apparatus adversely affects an imaging process. When a temperature difference occurs between the photoelectric conversion elements in the radiation imaging apparatus, a dark current varies from one photoelectric conversion to the other, causing a captured radiation image to be non-uniform. Particularly, a photoelectric conversion element used in the radiation imaging apparatus, which is mainly used to photograph a human body, is larger than an image sensor included in general video cameras. A temperature distribution in the radiation imaging apparatus greatly affects the quality of a captured radiation image. The captured radiation image is used for a medical practice, and hence the accuracy required of image quality is high. Thus, considering a temperature difference in the radiation imaging apparatus is important for designing the radiation imaging apparatus.
A flow of a cooling medium (air) in the radiation imaging apparatus greatly affects the temperature distribution in the radiation imaging apparatus. For example, when an electronic component having high heat is cooled by the heat radiation fan without taking into consideration the flow of air in the radiation imaging apparatus, the heated air flows to the other electronic components, thus heating those components. Consequently, the temperature distribution in the radiation imaging apparatus becomes non-uniform, adversely affecting the quality of a captured radiation image. If a discharge port for discharging the heated air from the radiation imaging apparatus is formed in an inappropriate position, an unexpected flow of air occurs in the radiation imaging apparatus, probably causing the heated air to heat the electronic components in the radiation imaging apparatus. Particularly, if a plurality of discharge ports is provided in the radiation imaging apparatus, external air frequently flows in and out, thus disabling prediction of a flow of air in the radiation imaging apparatus.
The technique discussed in Japanese Patent Application Laid-Open No. 10-177224 enables heat radiation suited to a driving condition. The technique discussed in Japanese Patent Application Laid-Open No. 2005-181922 enables heat radiation of the radiation imaging apparatus suited to a photographing condition by mounting the cooling unit according to the photographing condition. Both techniques are directed to higher efficiency of heat radiation. However, neither of the techniques gives any consideration to the flow of a cooling medium in the radiation imaging apparatus during capturing of a radiation moving image and, hence, both the techniques are unable to solve the problems caused by the temperature difference.